Keep fouling plugs... what do i need to change?

[YoungRicky27]

So im new to the 2 stroke engines and new to carbs. I have th ebig tumb screw on the carb about 1 1/2 to 2 tunes out. and i have been messing with the little gold screw on the air box side but i dont know what it does and where it should be. Where should both these screws be to srart? i wont idle longer then 10 sec when i have it warmed up. It was running hard then i started going fast and was crusing in 4th gear and then when i slowed down a bit it started to sputter and die, then it wont start agian till i get a new plug. please help as you guys have helped me so much already. could my mixture being wrong cause this problem? im running 40:1 because thats what my manul says. I just what this thing to run longer then 20 minutes. i ride a 87 lt250r

[Camoman]

I have the same problem, and i have been trying to gather information on the subject.
No it is not your mix ratio, it is the carb jetting. I'm not a carb guy , but I know on mine I have to drop the needle down a few clicks and put in a smaller main jet, still working on what size and where the Pilot jet is....I have a 240 main .

[dajogejr]

The thumb screw is for idle, you control idle speed with that.
The small brass screw is the air screw, you control low speed/partial throttle and idle mixture with that.

Turn the screw out to allow more air from idle to 1/4 throttle (leaner) and turn it in to allow less air (richer)

[nd4speed]

If this is the stock carb:

The gold brass screw should be no more than 3 turns out. This is the air screw already described.

The pilot is for idle to .25 throttle
The needle clip position is for .25 to.75 throttle
The main jet is for .75 to wide open.

Thumb screw pushes the slide up and is the same as pushing in the throttle.

Your plug should be dry and brown when done correctly.
I never changed my pilot and neither did my friend on his. Change clip position and main. Start with your main cause you don't even have to remove the carb just the float bowl plug. Buy smaller ones and start going down if your plug is black and wet.